adb-remount-test: Refactor raw remount & remount from scratch test

Move "raw remount test" right after "disable-verity -R test".
Device is expected to be in a clean state right after disable-verity, so
we can perform "raw remount test" immediately after. This saves us one
reboot.

Move "remount from scratch test" right before "remount -R test".
Since they both require overlay teardown state, group them together so
we only need to teardown (and reboot) once. This saves us one reboot.

Total test runtime reduced by two reboots.

Bug: 243116800
Test: adb-remount-test
Change-Id: Ifd95ba713f1819a7d31e88cd70077dc306c64c58